1. Technical Field of the Invention
The present invention relates generally to methods and apparatuses for manufacturing electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators.
More particularly, the invention relates to an apparatus and a method for shaping an electric wire for a stator coil of an electric rotating machine to form coil ends of the stator coil into a desired shape. Hereinafter, the coil ends denote the axial end portions of the stator coil which are located outside of slots of a stator core of the electric rotating machine.
2. Description of the Related Art
Generally, to increase the torque density of an electric rotating machine, it is necessary to improve the space factors of electric wires, which form a stator coil of the machine, by, for example, employing rectangular-cross-section wires as the electric wires. In addition, it is also necessary to minimize the coil ends of the stator coil which have almost no contribution to the generation of torque by the electric rotating machine. Further, the coil ends of the stator coil can be minimized by, for example, providing crank-shaped portions in the coil ends.
Japanese Unexamined Patent Application Publication No. 2003-264964 discloses a method of forming crank-shaped portions in the coil ends of a stator coil of an electric rotating machine. According to the method, an electric wire with a rectangular cross section is first shaped, using a first pair of male and female shaping dies, on a first plane to form a two-dimensional crank-shaped portion in the electric wire. Then, the electric wire is further shaped, using a second pair of male and female shaping dies, on a second plane which is perpendicular to the first plane to form a three-dimensional turn portion of the electric wire. The turn portion is to be located outside of slots of a stator core of the electric rotating machine and thus constitutes a part of the coil ends of the stator coil. The turn portion has a substantially triangular shape and includes the crank-shaped portion at the apex thereof. Next, with the turn portion being held between the second pair of shaping dies, the electric wire is bent at each end of the turn portion using a female bending die, thereby forming a pair of straight portions of the electric wire. The straight portions are connected by the turn portion and to be respectively received in two slots of the stator core. In addition, the interval between the straight portions of the electric wire defines a coil pitch of the stator coil.
With the above method, however, the stator coil is allowed to have only one coil pitch that is determined by the shape and size of the female bending die.
On the other hand, a stator coil of an electric rotating machine may be formed by first stacking a plurality of electric wires to form a flat band-shaped electric wire assembly and then rolling the electric wire assembly by a predetermined number of turns into a hollow cylindrical shape. In such a stator coil, the radius of each of the electric wires gradually increases from the inmost turn to the outmost turn of the stator coil. Accordingly, the stator coil is required to have a plurality of coil pitches that increase from the inmost turn to the outmost turn of the stator coil.
Therefore, when the method disclosed in Japanese Unexamined Patent Application Publication No. 2003-264964 is applied to shape the electric wires for forming the stator coil which has the plurality of coil pitches, it is necessary to employ a plurality of female bending dies having different shapes and sizes. As a result, the manufacturing cost of the stator coil will be increased. In addition, during the shaping process of each of the electric wires, it is necessary to replace the female bending dies the plurality of times, thereby increasing the time required for manufacturing the stator coil.